1. Field of the Invention
The present invention relates to a turbo generator having a stator and a rotor, a rotating bell type exciter connected to one end of the rotor, and being equipped with at least one cooler.
2. Brief Description of the Related Art
Large turbo generators for producing electric energy are designed as three-phase synchron machines having a stator and a rotor. One end of the rotor is connected to a turbo machine while the other end is connected to an exciter.
European patent application EP 1 443 639 A1 (see also U.S. Pat. No. 6,844,639) by the same assignee discloses the electrical function of a rotating exciter for large currents. The rotor has at least two conducting rods essentially parallel to the rotor axis and connected at their first end to a collector ring and connected at their other ends to individual rings via diodes of opposite polarity so that the a.c. current induced in the rods as a result of a static field is converted into a direct field in both rings.
One exciter type known in the art is the bell type exciter 3 as schematically shown in a partial sectional view in FIG. 6 herein. The turbo generator 1 has its rotor 2 connected to one end to the bell type exciter 3. The exciter 3 has multi-phase windings 4 rotating around a static portion 8. The exciter current is passed through diodes 5 to convert the alternating current into direct current and then fed into the respective rotor windings of the turbo generator 1. The rotating exciter is, in other words, the opposite of a generator. The windings of the static portion 8 of the exciter 3 are fed with direct current and the anchor is the rotating bell 10 of the exciter 3 producing alternate current.
The turbo generator 1 including the exciter 3 is on its lower portion based on the ground 6 and confined by a casing 9. Above the exciter 3 and opposite to the ground 6, one or more coolers 7 are arranged within the casing 9 to reduce the temperatures in the exciter 3 and thus increase the efficiency of the exciter 3.
One draw back of the prior art is that, in order to enhance the efficiency of the cooler and or to obtain redundancy in case of failure of one cooler, the number of coolers needs to be increased and/or the coolers need to be enlarged. This conflicts with limitations in space available at the respective site of the power plant. A further draw back of the prior art is the fact that the bell type exciter conveys cooling fluid from the center to its outer circumference. The tangential speed of this cooling fluid flow is quite high and the corresponding kinetic energy is lost.